If Ms$.$ Gonzalez borrows $$1000$ for $4$ years from a bank that charges $5\%$ annual simple interest, how much interest will she owe at the end of the four years? How much $($in total; interest $+$ principal$)$ will she pay to the bank at the end of the four years?

Joe is borrowing $$600$ from his parents in order to finish paying his tuition bill. His parents agree to the loan if Joe will repay the money at the end of nine months. His parents will charge him $3\%$ annual simple interest. How much interest will Joe owe his parents? How much will Joe have to pay his parents at the end of the nine months?

Find the amount needed to pay off a simple interest loan of $$5000$ at $6\%$ for $\frac{21}{2}$ years.

What amount needs to be invested today at $4\%$ simple interest in order to have $$6,000$ in $3$ years?